Post on 27-Jan-2016
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A System View on SKA Bandwidth Usage
G.W. (Dion) Kant
AAVP Dwingeloo, 14 December 2011
Outline
• Introduction• Overview of main envelope requirements• The concept of a base element• Bandwidth requirements
Introduction
• Details in Document “AA-MID CONCEPT DESCRIPTION”
• Presentation to initiate some discussion• A technology independent approach!
Introduction
• Where are we now?
Design Requirements
• Analysis of /, and Bandwidth.• A technology independent approach!• Select technology after understanding the
repercussions of the requirements
SKA2 / envelope
𝑇 𝑠𝑦𝑠=𝑇 𝑠𝑘𝑦+𝑇 𝑟𝑒𝑐
Consequence for
SKA2 Survey Speed envelope
SKA2 Resulting HPBW
Minimum required bandwidth
• Utilize concept of a base element:• Base element is an antenna element
which provides just the required FOV:– Main-Beam solid angle: – is effective area of base element– #(base) elements required to implement
Minimum required bandwidth
• Total aggregated bandwidth from base elements:
Survey spaced in terms of base elements
Bandwidth from base elements
SKA band (MHz)
Remark (m^2)
(degrees^2)
(MHz)
(THz)
70 < f < 450 1 band AA-low 6 380 102460
38.9
70 < f < 177 2 band AA-low 1 1 107 2650 0.284 177<f<450 2 band AA-low 2 6 272 11603 3.16 400<f<1450 AA-mid, because of
overlap based on .at f=500 MHz.
100 500 464198 232
400<f<1450 AA-mid alternative 100 @ 500 MHz
500 62500 29.2
1000<f<20000 Based on 15 m dishes and an efficiency of 0.7. FOV may be expanded by PAF technology. This does not meet the SKA2 requirements!
1000 4365 4.4
Physical element behavior
• Assume constant (aperture antenna)
• Inherent physical element behavior does not provide flat FOV!
• Current requirements demand spending processing to create flat FOV
FOV processing
• Described by using a concept of an artificial element with effective area not constant as function of subband channels
Station Bandwidth
• #signals to be transported per subband
Aggregated signal transport bandwidth
Bandwidth
• AA-mid aggregated signal transport bandwidth from (base) receptors & from stations
AA-mid band (MHz)
from receptors (THz)
from stations (THz)
Lowest: 400<f<900 232 48.96 Highest: 950<f<1450 232 161.3 Lowest: 400<f<900 (Alt.) 29.1 29.1 Highest: 950<f<1450 (Alt.) 29.1 29.1
Station processing mechanisms
• Two station processing mechanisms are identified:1. A lossless source coding retaining all
available information denoted as station beam forming reducing correlator load:
2. A lossy source coding which is reducing the available information denoted as FOV processing
An integral survey speed
• Current SS requirement is a spot frequency property. Bandwidth is not involved.
• A practical way to include bandwidth is defined (Integral Survey Speed)
• Provides a means to define spectral efficiency
Spectral efficiency
• Average survey speed encoded in one Hertz bandwidth (ISS/Btot)
AA-mid band (MHz)
(m4K-2sr Hz)
(m4K-2sr Hz)
(m4K-2sr)
(m4K-2sr)
Lowest: 400<f<900
Highest: 950<f<1450
Conclusion
• An analysis is presented of three key science requirements
• Analysis not based on specific technology• Current science requirements dictate huge
differences in resource requirements over the different SKA bands.
• Tailor science requirements for better usage of physical antenna properties
Conclusion (continued)
• Introduced the concept of a base receptor element to analyse bandwidth requirements
• Aggregated bandwidth is a measure for required processing
Conclusion (continued)
• Two different station processing mechanisms are identified:– Signal processing required for limiting
information in the spatial domain;– Signal processing required for reducing the
processing load of a correlator subsystem. This one can be considered as a lossless recoding of information in the form of station beam forming providing the station beams.
From the archives
From the archives
15 Years of SKA AA Concepts